1. Field of the Invention
The present invention relates to copper alloys, and particularly to alloys of copper containing boron, magnesium and tin as the alloying elements, and to a method for producing these alloys.
2. Description of Related Art
Heretofore, copper alloys containing beryllium as the sole or principal alloying element, referred to generally herein as copper beryllium alloys, have been employed in applications requiring the properties of high strength and high electrical conductivity. Beryllium is alloyed with the copper principally as a precipitation hardening agent, so as to improve the mechanical properties, particularly to increase the tensile strength of the copper.
Beryllium compounds have been shown to cause disease, and beryllium is recognized as a carcinogen, therefore, the use of beryllium as an alloying agent is being phased out at foundries in the United States. This has created a need for other high strength, highly conductive alloys, preferably copper-based alloys, for use in applications which have, prior to this time, primarily employed copper beryllium alloys.
Precipitation hardenable copper alloys and processes for producing copper alloys having high strength and/or high electrcal conductivity have previously been proposed. An example is presented in U.S. Pat. No. 4,434,016, which is directed to a precipitation hardenable copper alloy that includes a substantial quantity of nickel, and further includes aluminum, manganese, magnesium, and restricts the amount of silicon to very small amounts. The processing of this alloy to produce precipitation hardening in the alloy involves a complex series of steps requiring mechanical deformation to be performed.
Other alloys proposed in the prior art include the alloy disclosed in U.S. Pat. No. 4,338,130, which, in specifically avoiding the use of beryllium, employs not only nickel and silicon, but also requires aluminum and chromium to be present as alloying elements. Chromium has further been proposed in several other disclosures as being an alloying element in a precipitation hardenable copper alloy, or as an alloying element in a copper alloy that improves the mechanical properties through mechanisms other than precipitation hardening, such as dispersion hardening. Many of the prior art hardenable copper alloys depend upon the use of one or more steps of mechanical deformation to cold work the material in order to increase the mechanical properties sought for the alloy, at the expense of decreasing the ductility or formability of the alloys.
As noted in the '130 patent, the use of magnesium has traditionally been avoided, in that magnesium tends reduce electrcal conductivity and rease ductility. Magnesium is present in the copper-based alloy of the '016 patent and its presence indeed is disclosed as being critical, but the '016 patent expressly states that magnesium is not to exceed 0.5 wt.%.
Another beryllium-free copper alloy that has been employed in high-strength, high conductivity applications is designated as C81540. This alloy is a sand castable chromium-nickel-copper alloy containing 0.4-0.8 wt.% silicon, 2.0-3.0 wt.% nickel, 0.1-0.6 wt.% chromium, with the remaining balance being mainly copper, however, the specification permits minor amounts of other elements in the alloy. This alloy achieves its strength through the reaction of chromium and silicon, or nickel and silicon, or both.
There continues to exist a need for alloys that have relatively low additions of alloying elements, and that can be produced or processed in a simple manner, preferably without the need to conduct mechanical deformation steps, wherein the finished product has high strength and high electrical conductivity.
It is therefore a principal object of the present invention to provide a copper-based alloy composition having high strength and high electrical conductivity, while avoiding the use of beryllium as a precipitation hardening agent.
It is a further principal object of the present invention to provide a copper-based alloy composition that is precipitation hardenable to provide increased hardness and tensile strength, without the need to mechanically deform the material in obtaining those properties.
It is an additional principal object of the present invention to provide a precipitation hardenable copper based alloy in which relatively small amounts of specific alloying elements are employed.
It is an additional important object of the present invention to provide a copper-based quaternary alloy in which boron, magnesium and tin are essentially the only alloying elements.
It is a further principal object of the present invention to provide a process for producing a precipitation hardened copper-based quaternary alloy that includes a solution heat treatment followed by rapid quenching and then age hardening.
It is an additional important object of the present invention to provide a process for producing a precipitation hardened copper-based quaternary alloy as set forth in the preceding paragraph, and which does not require any steps of mechanical deformation or cold working to achieve the desired strength-properties.